Remove --tab-capture-upscale/downscale-quality.

content/browser/compositor/gl_helper.cc

Index: content/browser/compositor/gl_helper.cc
diff --git a/content/browser/compositor/gl_helper.cc b/content/browser/compositor/gl_helper.cc
index 55493e900689ba6bcf421056e29fefb1645ab875..2b89dfeead033dd86f7afdae045c70bf037bf6a5 100644
--- a/content/browser/compositor/gl_helper.cc
+++ b/content/browser/compositor/gl_helper.cc
@@ -182,7 +182,6 @@ class GLHelper::CopyTextureToImpl
                              GLHelper::ScalerQuality quality);
 
   ReadbackYUVInterface* CreateReadbackPipelineYUV(
-      GLHelper::ScalerQuality quality,
       const gfx::Size& src_size,
       const gfx::Rect& src_subrect,
       const gfx::Size& dst_size,
@@ -1181,7 +1180,6 @@ bool GLHelper::IsReadbackConfigSupported(SkColorType color_type) {
 }
 
 ReadbackYUVInterface* GLHelper::CopyTextureToImpl::CreateReadbackPipelineYUV(
-    GLHelper::ScalerQuality quality,
     const gfx::Size& src_size,
     const gfx::Rect& src_subrect,
     const gfx::Size& dst_size,
@@ -1201,6 +1199,20 @@ ReadbackYUVInterface* GLHelper::CopyTextureToImpl::CreateReadbackPipelineYUV(
   if (supported == GLHelperReadbackSupport::SWIZZLE)
     swizzle = kSwizzleBGRA;
 
+  // "The YUV readback pipeline is used by real-time video capture of
+  // tabs/windows/desktops.  Therefore, the scaler chosen here is based on
+  // performance measurements of full end-to-end systems.  When down-scaling,
+  // always use the "fast" scaler because it performs well on both low- and
+  // high- end machines, provides decent image quality, and doesn't overwhelm
+  // downstream video encoders with too much entropy (which can drastically
+  // increase CPU utilization). When up-scaling, always use "best" because the
+  // quality improvement is huge with insignificant performance penalty.  Note
+  // that this strategy differs from single-frame snapshot capture (i.e., using
+  // the Skia/RGB code path).
+  GLHelper::ScalerQuality quality = ((src_size.width() < dst_size.width()) &&
+                                     (src_size.height() < dst_size.height()))
+                                        ? GLHelper::SCALER_QUALITY_BEST
+                                        : GLHelper::SCALER_QUALITY_FAST;

[piman, 2016/04/06 18:32:47]

If SCALER_QUALITY_GOOD is not used any more, can you remove the enum and the
related code?

[xjz, 2016/04/06 18:44:05]

SCALER_QUALITY_GOOD is used as the default scaler in single-frame snapshot
capture:
https://code.google.com/p/chromium/codesearch#chromium/src/content/browser/co....
It provides nearly as good quality as "best" down-scaler, but much faster in
general.

[piman, 2016/04/06 19:20:07]

If that the case, then can you leave the policy decision (this line) out of
GLHelper, and to the calling code instead? The only advantage of baking it in is
if it can remove code. Since it can't, let's leave it outside for consistency
with other readback API?

[xjz, 2016/04/06 23:03:38]

Done.

   if (max_draw_buffers_ >= 2 && use_mrt) {
     return new ReadbackYUV_MRT(gl_, this, helper_->scaler_impl_.get(), quality,
                                src_size, src_subrect, dst_size, flip_vertically,
@@ -1212,7 +1224,6 @@ ReadbackYUVInterface* GLHelper::CopyTextureToImpl::CreateReadbackPipelineYUV(
 }
 
 ReadbackYUVInterface* GLHelper::CreateReadbackPipelineYUV(
-    ScalerQuality quality,
     const gfx::Size& src_size,
     const gfx::Rect& src_subrect,
     const gfx::Size& dst_size,
@@ -1220,7 +1231,7 @@ ReadbackYUVInterface* GLHelper::CreateReadbackPipelineYUV(
     bool use_mrt) {
   InitCopyTextToImpl();
   return copy_texture_to_impl_->CreateReadbackPipelineYUV(
-      quality, src_size, src_subrect, dst_size, flip_vertically, use_mrt);
+      src_size, src_subrect, dst_size, flip_vertically, use_mrt);
 }
 
 }  // namespace content